Perhaps this is a good excuse for buying and learning to play a 5 string. Just learn the songs in standard tuning otherwise. I play quite a few Eb songs in standard tuning no with no issues ( Rock With You, Do I Do). FWIW, I was in a similar predicament years ago. The solution that worked best for me was to learn theory well enough that I can basically play songs in any key any time. In addition to my main band, I sub in with friends bands from time to time and am forced to play songs in all sorts of different keys from what I am used to. Studying music seriously has helped tremendously. Let us know how you tackle this!